[clang] [clang-tools-extra] [clang-tidy] Avoid matching nodes in system headers (PR #151035)

[Carlos Galvez via cfe-commits]

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@@ -105,6 +105,10 @@ Improvements to clang-tidy
   now run checks in parallel by default using all available hardware threads.
   Both scripts display the number of threads being used in their output.
 
+- :program:`clang-tidy` no longer attemps to analyze code from system headers
+  by default, greatly improving performance. This behavior is disabled if the
+  `SystemHeaders` option is enabled.
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carlosgalvezp wrote:

`SystemHeaders` means analyze **and** warn about system headers. Renaming the option is a much larger scope since it's a user-facing option, which requires a 2-release cycle to rename.

Or perhaps the comment was intended for the new `SkipSystemHeaders` option in `MatchFinderOptions`?

https://github.com/llvm/llvm-project/pull/151035